Return-Path: Date: Thu, 15 Mar 2018 09:32:09 +0100 From: Lukas Wunner To: Hans de Goede Cc: Marcel Holtmann , Gustavo Padovan , Johan Hedberg , =?iso-8859-1?Q?Fr=E9d=E9ric?= Danis , linux-bluetooth@vger.kernel.org, linux-serial@vger.kernel.org, linux-acpi@vger.kernel.org Subject: Re: [PATCH 4.16 REGRESSION fix 1/2] Revert "Bluetooth: hci_bcm: Streamline runtime PM code" Message-ID: <20180315083209.GA21373@wunner.de> References: <20180314220603.7559-1-hdegoede@redhat.com> <20180314220603.7559-2-hdegoede@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180314220603.7559-2-hdegoede@redhat.com> List-ID: On Wed, Mar 14, 2018 at 11:06:02PM +0100, Hans de Goede wrote: > This reverts commit 43fff7683468 ("Bluetooth: hci_bcm: Streamline runtime > PM code"). The commit msg for this commit states "No functional change > intended.", but replacing: > > pm_runtime_get(); > pm_runtime_mark_last_busy(); > pm_runtime_put_autosuspend(); > > with: > > pm_request_resume(); > > Does result in a functional change, pm_request_resume() only calls > pm_runtime_mark_last_busy() if the device was suspended before the call. > > This results in the following happening: > > 1) Device is runtime suspended > 2) Device drives host_wake IRQ logically high as it starts receiving data > 3) bcm_host_wake() gets called, causes the device to runtime-resume, > current time gets marked as last_busy time > 4) After 5 seconds the autosuspend timer expires and the dev autosuspends > as no one has been calling pm_runtime_mark_last_busy(), the device was > resumed during those 5 seconds, so all the pm_request_resume() calls > while receiving data and/or bcm_host_wake() calls were nops > 5) If 4) happens while the device has (just received) data in its buffer to > be read by the host the IRQ line is *already* / still logically high > when we autosuspend and since we use an edge triggered IRQ, the IRQ > will never trigger, causing the device to get stuck in suspend > > Therefor this commit has to be reverted, so that we avoid the device > getting stuck in suspend. > > Cc: Lukas Wunner > Signed-off-by: Hans de Goede Acked-by: Lukas Wunner